Screw propeller



March 0- 'w. BAUMANN I 2,193,616

SCREW PRbrELLEn Filed June 29, 1938 2 Sheets-Sheet 2 9 INVENTOR 772mb m AT RNEYS Patented Mar. 12,

UNITED STATES The ffic'iency of shin prapengijap'pr e'ciiably smaller than the efiioiency of propellers of water turbines. 'Ihisdifferenc e is due to the shape the blades and thedehiessioneaujsled by-thelhub. The inost advantageous sharia of thebl'ades would be that of the lifting' surfaes of aero dynamics, but-the application of theseiorms has been imposs'ibl e'until now, the reason being that the sn'iall hubs forced constriictors to eert'rm the bases of the blades for reasons" oiresistan'oe and in order to decrease the suction effect caused by the rotation of the blades. t

A proposal decri'bed in tlije Frenchlatnt No.

736-1536 seeks to harmonize these two oonditijo'ns' 5" providing a hub that maj have u'p to 3 5 of the optimum di ame ter of. the probeller In other proposals an attempt is made-to lessen the importance of the v orte'x supplying atmosv pherio air to the reariac'e of' thebhuhlse thej French Patent NO. 776,656 and British Pafifl em 3 57 y .It has even'been proposed, th'fo' tq h ef st o nd e iwl flee P we the-blades wherea depression might not of he bl i 5 hertmod l ee eflect about 'the' hub and do not permit the app iQation 'of blades with lifting suriaces.

I By the present invention ithe 3H referred to are avoided, and a ;construc r d w i d l e w t .irsimi t e ente or ft P op e b llu iep ei..h i ;h ving a diameterwhiohis mad at last,j {l0%@or more of the effective diameter oi thepro 'eller;

3'5" The use of ahu b of such diameter'makes it possible toemploy six-or morefblaide's "and to give the same aprofile having the contoiitof'the best knownlifting surface, i.'e'., 0'ne' having anearly uniform thickness and debthQo /fer the greater h p-tram s its act i'vepart. I BY me ns of n uc n .dev ce w ch wil be referred to later, on; theye'ntilation by the" atmospheric 'air of the whole surfaceoi the'hub U and 'of the base of the bladeslis effected, a not only' the rear face of the n t, the air .beingiat' the same time preventedfroinhentrating along the back of the blades tome-places where a de'- pression might be produced This arrangement require 50 air which could. not beoonduoted toth"prob er through a hollow shaft or? hollow hub without creating in this feed conduit a depression that would be such' as to arm ventilation. a, r H 1-; According to the present invention the an of a tag"- 26 These two proposals do not provide a spin costof upkeep tthe shaftjsolthat in'spite'of the may little water i l n er t e ch mbe -film cond s 4,0"

a great vbmm" of 1' the benefit of the ifentilation is a conduit having a cliametergreater than' that oi the propeller hub.

:The conduit, which isnmde of sheet' metal thick en h to. i t nd the ressure p v he at is fixeduto the vjes's'ela ncl surrounds the end of thel n u aw ii ie mt iie r touch the blades; In this manner an annular space of M large section is, formed between the hub and the conduit; Qwingtothi's' arrangement,yvhieh-is of capital importance, the hub and the baseofothe 10 blades are c mplete' Iy separated b ythe air iro rn the Water; which makes it possi e tostrengthen I the profilesfla t tli ba ""pord rig to the needs of their-resistance without, having. to trouble ciency since 'thepropellerbases nolonger fu;-

rush mbtivwor'k; e

.Thh'eirintm uen d vi e cl enbty r in; the rotation, a es not need any stuffing boxfl and hasj'no c'o ct with them i shaft or the 20 expans' ns and Vibrations have no x i' lldi r i no o q be n n, r ew. c 'e lw s. bs rb metive forcejandis responsible for wear and'a' certain continued as atube disposed in' the int ez'ior of the boat and extends above the water lineas in "thearrangementshown. lithe ma n shaft has 3'6 7 an egt rnai its support, is hollow for this purpose andconneoted to the air cha nj 's rre d n theb eri will s n e as the i conduit. The air chamb which has a hydrodynamic shape, opefisjlbelow in th el central region f p fbi hr eel yc b eel gain ther amend the shaft" by n eans" of a collar haying a certain new nd e urr hd by e i e t nt g w th veja e. ect n n o id i. o; n e,

'atmojspheri'canf to thepropeller witha minimum according toj the present invention, requires 10 4 5 b61 15 m of a1; per se pond, d it, will thus be understoodthat it is ijmpossibletointroduce this .v'ol' e' of air through a shaft with a hollow 151"tnioisol inoneof the previously cited a en t t v present invention thin ribs are, provideddnth. twojaces'ofeach pi opeller blade at the" level o'f the' wallof the air'conduit, in order 7 toe irteiid thea'ctiori ofthe'co duit to the whole siiiface'oi the hub. "I'liepurpdse'of the ribs is 55"" to prevent on the one hand the water from approaching the hub at the points where the water pressure exceeds the centrifugal force of the incipient vortex, and to prevent on the other hand the radial displacement of the air along the back of the blades.

ther objects of the invention will in part be obvious and will in part appear hereinafter.

The invention accordingly comprises the features of construction, combination of elements and arrangement of parts, which will be exemplified in the construction hereinafter set forth and the scope of the invention will be indicated in the claims.

For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description taken in connection with the accompanying drawings, in which:

Fig. l is a longitudinal section showing the stern of a boat equipped with propelling means in accordance with the invention;

Fig. 2 is a fragmentary sectional view taken on the line 2-2 of Fig. 1;

Fig. 3 is a fragmentary sectional view taken on the line 3--3 of Fig. 1, and shows the profile of a blade of the character employed in the present invention;

Fig. 4 is a sectional view similar to Fig. 1 but showing a modified form of theinvention;

Fig. 5 is a fragmentary perspective view showing another modified form of a propeller provided in accordance with the invention;

Fig. 6 is an explanatory diagram;

Fig. '7 is a sectional view taken on the line 1-'l in Fig. 5; and 1 Fig. 8 is another sectional view taken on the line 88 in Fig. 5. I

Referring now to the drawing, and particularly to Fig. l, a fragment of the ships hull is shown at e from which extends a driving shaft a having affixed to its outer end hub 12 that carries a plu-, rality of propeller bades c, the hub being retained in place by means of a nut b. air for the huh I) is conveyed by a conduit comprising a tubular wall d that extends outwardly from and is supported by the hull and surrounds shaft a. the conduit d by means of a tube f disposed within the ships hull. 1

As the intensity of the vortex is proportional to the square of the speed of rotation, it becomes small for low speeds, which is the reason why the air at low speed does not surround the hub; it is therefore useless to give the nut .b' a hydrodynamic form in order to diminish the suction which a surface perpendicular to the axis might exhibit at low speed. The ribs c, 'cf are disposed one on each side of blade c and are arranged to follow up the wall (1, but they may be placed a little closer to or a little farther from the axis and their inclination may vary within the limits of the region where a partial vacuum may start.

According to the embodiment shown in Fig. 4, d is the wall of the air chamber, 9 the bearing, d the annular part of the air chamber, d" a collar, a the sleeve integral with the shaft.

The air reaches the chamber through the suspension h of the bearing forming an air conduit.

The greatest diameter of the hub must be ad- -iacent the end of the air chamber. and diminish The ventilating The air for ventilation is suppliedto.

water does not close again immediately behind the air chamber, if only on account of the speed of the boat through the effect of inertia, the inertia would be sufficient to create a vacuum around the hub in the first third of the propeller even if there were no vortex. After the first third the effect of the centrifugal force asserts itself. In the two cases the ribs are useful and their effect varies according to their shape and height.

It must be pointed out that by increasing the number of the blades the propeller becomes less subject to vibrations than propellers having two, three or four blades, its efliciency being therefore enhanced.

' On the other hand, the present invention makes it possible to arrange the external bearing closer to the propeller without creating harmful vortices the bearing being in the interior of the chamber.

The advantages springing from the principle of the total ventilation of the center of the propeller are shown in a still more concrete shape by the following constructional features,

The bases of the metal blades may be cut away in such a way that the wall of the air chamber can be put in deeply. The front edge of the blades. then extends beyond the edge of the air chamber, so that the wall of the chamber penetrates this region where the radial displacements of the air or the water are most to be feared.

Fig. 5 shows an embodiment of the invention employing blades cut away at their forward edge in the manner indicated. Here. the blade 0, shown as extending upwardly from the hub 12. has its forward edge cut away to provide a relatively deep notch 22" at a point adjacent the hub. Into this notch the wall d of the air conduit extends, the clearance provided admitting of but little play. The fin on the side of the blade, which guides the air from the conduit over the huh I), is shown at c.

Fig. 6 illustrates a principle to be observed in achieving proper design for the profiles of blades provided in accordance with the invention. The radius about which the blade is generated, shown at g in Fig. 5, is also denoted g in Fig. 6. The trace of the chord of a profile is shown as a point gonradius g, the normal section of the profile being accordingly shown at h. This section is in effect displaced to the position shown at 71" by the instantaneous velocities indicated by the arrows in Fig. 6. The blade may then be generated by moving a profile of a section which is substantially uniform adjacent the hub but slopes away from the forward edge so as to reduce the mass and thickness of the blade. This is shown more particularly in Figs. '7 and 8.

The profile in Fig. '7 is drawn on the base of the wetted part of the blade. This profile is carried to the outside on the radius 9 passing through the center of the chord g of the lower profile, while giving it an angle of incidence corresponding to its distance from the center of the propeller. It is recommended to leave the lower profile h'for manufacturing and efllcicncy reasons. On the other hand the upper profile f2" which follows the course 9 will be progressively inclined during the advance toward the outside; in this manner the profile is reduced and the one illustrated by Fig. 8 is obtained. This solution offers great advantages in founding with respect to molding,

It is of course important to make the play between the wall of the air chamber and the blades of the propeller'as slight as possible.

In the practice of the present invention, care should be taken to annul the effect of a possible electrolytic corrosion by selecting for the edge of the air chamber a metal or facing of suitable material, which is easy to apply as there is no contact between the air chamber and the rotating body.

The inlet of theair conduit which is necessarily placed above the surface of the water, may be inside the vessel or on the outside, according to regulations and the desire of the constructor.

Thus the system here proposed enables one to make the blades of very Slight depth and to employ speeds at which the belly of the blade becomes the only active surface and the back is soto-speak no longer in contact with the water. While there is a substantially complete absence of water in the space directly surrounding the hub, due to the presence of the air blown over the hub as herein provided, it is possible for a little air to escape at the back of the blades, and to avoid this, the pressure is increased above atmospheric by a small amount, for example, .2 to .3 of an atmosphere. There will therefore no longer be any vaporization and condensation, which are the principal agents of the wear of cavitation. On the other hand, it is not possible to create a depression on the back of the blade beyond the vacuum, while it is possible to increase pressure on the belly without impairing as new and desire to secure by Letters Patent is:

1. In a construction for screw propellers for ships and the like, the combination with a hub of powered from a point within the ships hull, of

a plurality of blades secured about said hub each of which has the profile of an aerodynamic lifting surface, an air sleeve of diameter greater than said hub disposed about said shaft and positioned to discharge air rearwardly over said hub, and fins on said blades, one on each side and positioned to be in line with the'wall of said air sleeve and serving as continuations thereof over said hub.

2. In a, construction for screw propellers for ships and the like, the combination with a hub of a diameter at least 40% of the effective diameter of the propeller provided with a driving shaft powered from a point within the ships hull, of a plurality of blades secured about said hub, each of which has the profile of an aerodynamic lifting surface, an air sleeve of diameter greater than said hub disposed about said shaft and positioned to extend rearwardly a slight distance over the forward end of said hub, and fins on said blades,

one on each side and positioned to be in line with the wall of said air sleeve andserving as continuations thereof over said hub.

13. In a construction for screw propellers for ships and the like, the combination with a hub of a diameter at least 40% of the effective diameter of the propeller provided with a driving shaft powered from a point within the ships hull, of

a plurality of blades secured about said hub, each of which has the proflle'of an aerodynamic lift-' sleeve penetrating therein, and fins on sai'dblades,

one on each side and positioned'to be in line with the wall of said air sleeve and serving as continuations thereof over said hub.

4. In a construction for screw propellers for,

ships and the like, the combination with a hub of a diameter at least 40% of the effective diameter of the propeller provided with a driving shaft.

powered from a suitablepoint, of a plurality of blades secured about said hub, each of which has the profilelof an aerodynamic lifting surface, an air sleeve of diameter greater than said hub disposed in advanceof and concentrically with said propeller and arranged to discharge air rearwardly over said hub, and means associated with said propeller for causing air issuing from said sleeve to envelop said hub and completely. displace water from about'the same.

5. In a construction for screw propellers for ships and the like, the combination with a hub of a diameter at least 46% of the effective diameter of the propeller provided with a driving shaft powered from a suitable point, of a plurality of blades secured about said hub, each of which has the profile of an aerodynamic lifting surface, an airsleeveof diameter greater than said hub disposed in advance of and concentrically with said propeller and arranged to discharge air rearwardly over said hub, and recesses cutinto said blades adjacent said hub at the forward edges of said blades; said air sleeve being arranged to extend rearwardly and penetrate sufficiently into said recesses in order that the air supplied about said hub may completely envelop the same.

6. In a construction for screw propellers for ships and the like, the combination with a propeller hub of hydrodynamic form and having a driving shaft provided with an external bearing, of a plurality of blades having an aerodynamic profile secured about said hub, an air chamber having a discharge sleeve of diameter greater than said hub disposed about said shaft and external bearing, said chamber having an external streamlined contour and provided with an air supplying conduit, and fins on said blades positioned near nations of the wall of said air sleeve over said-hub.

'7. In a construction for screw propellers for ships and the like, a blade of aerodynamic form as calledfor in claim 1, in which the profile of the innerwetted portion adjacent the hub is substanslopes awayfrom the forward edge so as to reduce the mass and thickness of the blade.

WERNER BAUMANNh the base thereof and arranged to serve as contin- 

